Method for forming a colored coating on aluminous materials

ABSTRACT

Colored oxide coatings from yellow to brown on aluminum or aluminum alloy are formed by an anodic oxidation with an aqueous solution of 0.5 - 10.0 percent by weight of oxalic acid and 0.05 - 4.0 percent by weight of an ammonium salt, a metal acetate or a metal nitrate.

United States Patent Ikegaya et a1.

' Jan. 14, 1975 METHOD FOR FORMING A COLORED COATING ON ALUMINOUSMATERIALS [75] Inventors: MasashiIkegaya;Fumio Shigeta,

both of Shizuoka,Japan [73] Assignee: Riken Light Metal Industries Co.,

Ltd., Magarikane. Shizuoka, Japan [22] Filed: July 27, 1972 [21] Appl.No.: 275,821

[30] Foreign Application Priority Data July 30, 1971 Japan 46-57348 Aug.21, 1971 Japan 46-63337 Aug. 21, 1971 Japan 46-63338 Aug. 21, 1971 Japan46-63339 52 US. (:1. 204/58 [51] Int. Cl C231) 9/02 [58] Field of Search204/58 [56] References Cited UNITED STATES PATENTS 1,735,286 11/1929Kujirai et a1. 204/58 Nagata 204/58 OTHER PUBLICATIONS The SurfaceTreatment and Finishing of A1 and its Alloys by Wernick et al., 3rd Ed.,1964, p. 363. Surface Treatment of Al & its Alloys," Wernick et al., 3rdEd., 1964, pp. 306, 758759.

Primary ExaminerR. L. Andrews Attorney, Agent, or FirmEric l-l. Waters[57] ABSTRACT Coloredoxide coatings from yellow to brown on aluminum oraluminum alloy are formed by an anodic oxidation with an aqueoussolution of 0.5 10.0 percent by weight-of oxalic acid and 0.05 4.0percent by weight of an ammonium salt, a metal acetate or a metalnitrate.

7 Claims, N0 Drawings METHOD FOR FORMING A COLORED COATING ON ALUMINOUSMATERIALS The present invention relates to a method for forming acolored oxide coating on the surfaces of aluminum or aluminum alloymaterials and particularly a method for forming a colored oxide coatinghaving a broad yellowish color tone on aluminum or aluminum alloymaterials by an anodic oxidation.

In the specification, aluminum or aluminum alloys are referred to asmerely aluminous material(s).

Recently, aluminous building materials have been utilized broadly,because aluminous materials have excellent abrasion resistance andweather resistance and fulfill the requirements desired of buildingmaterials and have a beautiful appearance and a broader coloration rangethan the other metal materials.

However. it can be said that, while the coloration range of aluminousmaterials is broader than that of the other metal materials it is notalways possible to color such aluminous materials in various color tonesto the maximum desired extent. Thus, various investigations have beenmade to widen the color tone but a satisfactory method which can colorthe aluminous materials to the color tones desired by the user andparticularly to a broad range of yellowish color, has never heretoforebeen developed. Among the processes known for coloring aluminousmaterials yellow are the following features:

l. Oxalic acid is used as an electrolytic bath.

2. Anodic oxidation is effected in an electrolytic bath containing anaromatic sulfonic acid and sulfuric acid or a metal sulfate.

3. An aluminous material is previously subjected to an anodic oxidationand then applied with an alternate current in an electrolytic bathcontaining a metal salt.

In any of the above known processes, the obtained range of the colortones is narrow and for example, in the above described first processwhich is the most practical process among these known processes, thecolor tone of the obtained oxide coating is of a very narrow range andeven if the thickness of oxide coating or the quality of aluminousmaterials is varied, the remarkable variation in color cannot beobtained. Accordingly, colored oxide coatings having the broad yellowishcolor tone required by the user, have not heretofore been obtained.

The above described second and third processes can provide oxidecoatings having a relatively broad color tone but the second processuses an electrolytic bath consisting mainly of an aromatic sulfonic acidwhich is a specific chemical and therefore the electrolytic bath isexpensive. In the third process, after the usual anodic The presentinvention aims to solve the above de- I scribed deficiencies andprovides a method for producing colored oxide coatings of aluminousmaterials wherein colored oxide coatings of aluminous materials having abroad yellowish color tone are formed by an anodic oxidation using'anelectrolytic bath having a simple composition.

For the practice of the method of the present invention, firstly, analuminous material to be treated is degreased with an aqueous solutionof sodium hydroxide and then washed with water and successivelyneutralized in an aqueous solution of nitric acid and then washed withwater. Then, the thus treated aluminous material is subjected to ananodic oxidation with direct 5 current by using an aqueous solutioncontaining 0.5 10.0 percent by weight of oxalic acid and 0.05 4.0percent by weight of ammonium salt, 0.05 1.5 percent by weight ofacetate or 0.05 0.7 percent by weight of nitrate as an electrolyticbath.

In this case, the above limitation of the composition of theelectrolytic bath is based on the following reason.

The addition of oxalic acid serves to improve the electric conductivityof the bath and facilitate the electrolysis, whereby the yellow oxidecoating is formed on aluminous materials. This has been previously knownas shown in the above described first process. Accord ingly, for thesame reasons as in the above first process, oxalic acid is added as anessential component of the bath, i.e., in order to obtain the yellowcolor tone and at least 0.5 percent of oxalic acid is necessary togenerate the yellow color; when the amount of oxalic acid is larger than10.0 percent, the dissolution of such an amount of oxalic acid isdifficult at room temperature.

The addition of ammonium salts, acetates or nitrates serves to widen thecolor range of the oxide coating on aluminous materials and to obtain anyellowish color tone and these salts improve the luminosity. An amountless than the lower limit cannot develop the effect of addition, whileeven if amounts more than the upper limits are added, the effect ofcoloration does not vary. It has been found that these ranges canprovide colored oxide coatings of a broad color tone from yellow togreyish yellow.

As an ammonium salts, use can be made of ammonium phosphate and ammoniumdichromate.

As acetates, use can be made of manganese acetate and chromium acetate.

As nitrates, use can be made of ferric nitrate and chromium nitrate.

The optimum conditions when aluminous materials are treated by definingthe bath composition to the above range are as follows:

oxidation, an alternating current must be applied and consequently thereare problems in view of productivity and cost.

It is assumed that in the above described bath composition, oxalic acidcontributes to the hue of the oxide coatings and that the metal saltsprovide an auxiliary contribution. Furthermore, it is assumed that themetal salts mainly contribute to the luminosity range of the coloredoxide coating.

The following examples are given for the purpose of illustration of thisinvention and are not intended as limitations thereof.

Example 1 An aluminous material 1,100 was immersed in 7.5 percent byweight of an aqueous solution of sodium hydroxide at 80C for 30 secondsand washed with water and then the thus treated aluminous material wasimmersed in 10 percent by weight of an aqueous solution of nitric acidto effect neutralization and washed with water.

The thus pretreated aluminous material was anodized as an anode in anelectrolytic bath of an aqueous solution containing oxalic acid andstannous sulfate as shown in the following Table 1 at a temperature of20:1C. with a direct current of a current density of 2 A/dm and avoltage of 30 105 V for 60 minutes to obtain colored oxide coatingsshowing greyish yellow as shown in Table 1.

Table 1 Composition of electrolytic bath Voltage Thickness (it byweight) (V) of coating Color tone* Oxalic Stannous t) acid sulfate 0.160-85 29 2.6 G 4.6/1.9 0.1 55-75 31 4.2 GY 5.4/1.7

5 0.75 35-45 30 4.6 GY 515/l.5

Munsell notation When ferrous sulfate was used instead ofstannoussulfate. the similar results were obtained.

Example 2 The same aluminous material as used in Example 1 waspretreated in the same manner as described in Example l. The pretreatedmaterial was anodized as an anode in an electrolytic bath of an aqueoussolution containing oxalic acid and titanium sulfate as shown in thefollowing Table 2 at a temperature of 20ilC with a direct current of acurrent density of 2 A/dm and a voltage of 30 95 V for 60 minutes toobtain colored oxide coatings showing greyish yellow as shown in Table2.

Table 2-Continued Composition of The same aluminous material as used inExample 1 was pretreated in the same manner asdescribed in Example 1.The pretreated material was anodized as an anode in an electrolytic bathof an aqueous solution containing oxalic acid and manganese sulfate asshown in the following Table 3 at a temperature of 20flC with a directcurrent of a current density of 2 A/dm and a voltage of 30 V for 60minutes to obtain colored oxide coatings having a color tone rangingfrom amber to brown as shown in Table 3.

Table 3 Composition of Thickelectrolytic bath Voltage ness of (7} byweight) (V) coating Color tone* Oxalic Manganese 11-1.)

acid sulfate 1 0.10 60-85 30 245 G 4.4/1.6 1 0.20 55-75 31 4 G 4.0/2.0 20.20 55-74 30 9.3 GY 4.2/1.7 2 0.25 45-67 30 910'GY 4.0/1.9 3 0.25 40-5830 8.0 CY 4.5/1.7 3 0.50 40-48 32 7.5 CY 4.1/1.9 3.5 0.25 40-60 31 5.0CY 4.2/1.7 3.5 0.50 40-54 32 6.8 GY 4.0/1.8 3.5 -0.75 40-48 32 7 2 GY41/1.8 4.0 0.25 40-63 29 2 9 GY 6 8/1.3 4.0 0.50 40-55 32 5.2 GY 5 2/144.0 0.75 40-46 32 6 8 GY 4 8/15 5.0 0.10 40-69 31 20GY 72/12 5.0 0.2540-65 31 3 s GY 6 11/15 5.0 0.50 35-53 32 4 GY 54/16 5.0 0.75 35-48 32 45 GY 5 4/l.4 10.0 0.50 30-46 32 3.0 CY 7.4/1.2 10.0 0.75 30-43 32 4.2 CY7.0/1.2 10.0 1.00 30-45 30 6.6 CY 6.2/1.4

'Munsell notation Example 4 In this example, the influence of thequality of aluminous material upon the color tone and thickness of theresulting coating was examined. Various aluminous materials as shown inthe following Table 4 were anodized as an anode in an electolytic bathof an aqueous solution containing 3 percent by weight of oxalic acid and0.5 percent by weight of manganese sulfate at a temperature of 20i1Cwith a direct current of a current density of 2 A/dm for 60 minutes toobtain a result as shown in Table 4.

Table 4' Table o- Continued Alumi- Highest volt- Thickness Composition fi fi U f t, c I l electrolytic bath Voltage ness of :1 y age a e o coaing 0 or one 5 v v 3 (AA) electrolysis UL) z by weight) (V) coatingColor tone v Oxalic Ammonium 1.)

acid dichromate 48 32 GY 3 0.3 50-80 29 0.1 GY 5.4/2.4 3003 52 30 3 G42/19 0 7 50 135 30 2 9 GY 5 a 17 5052 49 30 7.1GY 4.6/1.6 10 I 6063 4932 CY MA 1.5 100-150 31 1.0 GY 61/109 0.05 45-60 211 7.0 Y 5.9/3.2 Mumll0.3 45-60 28- 7.4 Y 5.9/2.5

Example 5 1.5 50-115 29 9.1 Y 5.4/2.5 3.0 110-135 31 4.6(1Y 57/19 Thesame aluminous material as used in Example 1 222.- was pretreated in thesame manner as described in Ex- 4 Munsell 11661116 ample l. Thepretreated material was anodized as an anode in an electrolytic bath ofan aqueous solution containing oxalic acid and ammonium phosphate asExample 7 Show In the followmg Table 5 at a tfimperature of The samealuminous material as used in Example 1 0 Wlth a direct Current of aCurrent l y of 2 was pretreated in the same manner as described in Ex-A/drp anld a voltage of 6t) 150 for 60 m nutes to mple l. The pretreatedmaterial was anodized as an Obtim CO 9? a Coanngs Showing yellowlsh grewanode in an electrolytic bath of an aqueous solution as S awn m v a econtaining oxalic acid and manganese acetate as shown Table 5 in thefollowing Table 7 at a temperature of 20ilC I with a direct current of acurrent density of 2 A/dm Composition of Thickand a voltage of 130 V forminutes to obtain electrolytic bath Voltage ness of l 2 byweigm (v)coating Colormny 30 co ored oxide coatings having a color tone rangingoxalic Amflwmum from yellow to dark yellowish green as shown in Tableacid phosphate 7 0.1 85-140 30 7.7 GY 4.7/1.6 Table 7 0.1 60-85 30 2.7GY 5.4/3.0 35 0.3 -85 .31 1.3 GY 5.2/2.2 Composition of Thick- 3 0.5 -9031 0.3 GY 5.3/2.3 i 1 9 K g nessof (L75 x5 95 32 2'5 GY 5.5/1.9 y weigt) (V) coating Color tone 1.0 A 95-110 31 7.4 CY 4.7/1.8 (W3 r' 5 15110-90 29 2.11 GY 5.0/1.11 10 1.5 60-70 29 7.4 Y 5.7/2.9 40 M5 80420 295] Y S's/" 7 1 0.1 -115 30 2.4 CY 5.7/l.8 'Munscll notaiion 0.05 60-7529 7.3 Y 5.8/2.7 EXample 6 45 0.1 60-80 .29 7.7 Y 5.7/2.7 The samealuminous material as used in Example 1 3 03 -130 31 83 was pretreatedin the same manner as described in Ex- 05 -130 31 GY 9 ample 1. Thepretreated material was anodized as an 0.7 32 5.4 GY 5.4/1.2

' (constant) anode n an electrolytic bath of art aqueous solution m 325'2 GY 56/ containing oxalic acid and ammonium dichromate as 50 0.0550-60 28 7.2 Y 5.7/3.i shown in the following Table -6 at a temperatureof c 5 0.7 50-65 28 8.2 Y 5.6/29 20:1 C with a direct current of acurrent density of 2 10 0 O5 45 55 27 7 I Y 5 3 A/dm and a voltage of 50V for 60 minutes to 0 l obtain colored oxide coatings having a colortone rang- 5 28 Y ing from yellowish green to greyish yellow as shown in55 ,Munseu mum, Table 6.

Table 6 Example 8 Composition Of Thick- The same aluminous material asused in Example 1 ball 60 was pretreated .in the same manner asdescribed in Ex- (7r by weight) (V) coating Color tone Oxa|ic Ammonium(IL) ample The pretreated material was anodized as an acid dichromateanode in an electrolytic bath of an aqueous solution 005 80430 30 3'5 GY5'7/6 containing oxalic acid and chromium acetate shown 1 OJ 25435 30 82Gy 56/11 65 in the following Table 8 under the same condition and 0.370-80 28 6.9 B6 5.6/1.6 procedure as described in Example 1 to obtaincolored 0.5 60-75 2 B 52/18 oxide coatings having a color tone rangingfrom yellow 0.05 50-80 29 8.6 Y 5.6/2.7

to dark yellowish green as shown in Table 8.

Table 8 Composition of Thickelectrolytic bath Voltage ness of (9? b igL(V) coating Color tone* Oxalic Chrot) mium acid acetate 1 0.05 75-130 314.3 CY 5.6/1.8 i i 7 0.05 (ll/ 30 I f muflrwwlkmfi (1.1 60-80 30 9.0 Y5.6/2.6 3 (1.5 o iiif 56 E v Q/TT i 1:5 65-1 10 31 1.0 (W 5.2/2.4

5 0.05 55-70 28 5.1 GY 5.6/2.7 7.5 0.05 50-60 28 5.6 Y 5.9/3.1

Munsell notation Example 9 The same aluminous material as used inExample 1 was pretreated in the same manner as described in Example l.The pretreated material was anodized as an anode in an electrolytic bathof an aqueous solution containing oxalic acid and ferric nitrate asshown in the following Table 9 at a temperature of ilC with a directcurrent of a current density of 2 A/dm. and a voltage of 1 10 V forminutes to obtain colored oxide coatings showing greyish yellow as shownin The same aluminous material as used in Example 1 was pretreated inthe same manner as described in Example l. The pretreated material wasanodized as an anode in an electrolytic bath of an aqueous solutioncontaining oxalic acid and chromium nitrate as shown in the followingTable 10 at a temperature of 22- -lC with a direct current of a currentdensity of 2 A/dm and a voltage of 45 110 V for 60 minutes to obtaincolored oxide coatings showing greyish and yellowish green as shown inTable 10.

Table 10 Composition of electrolytic bath Voltage Thickness ("/1 byweight) (V) of coating Color tone* Oxalic Chro- .1.)

mium acid nitrate l ().05 -110 29 (1.7 CY 5.7/1.8 3 0.05 60-75 2) A 1.9CY 5.6/2.1 .2 .....fl9: l9 v.31 ..l Q. .Qifl ...Z;l... .?.l(. 1l 0.5045-50 28 1.2 (lY 6.2/2.1

' Munscll notation As described above, in the method of the presentinvention, an aluminous material which has been previously degreased andwashed with water is anodized in an electrolytic aqueous bath containingoxalic acid and a metal salt to obtain a colored oxide coating.Therefore, the method of thepresent invention has the following merits.

1. Electrolyte is inexpensive.

2. High technique is not required.

3. Efficiency is high.

4. Oxide coatings having a broad range of color tone from yellow tobrown can be obtained.

That is, the above merit l is that the electrolytic bath 0 is composedof usual chemicals and therefore the cost LII lit

is inexpensive, and the above merit (2) is that satisfactorily coloredoxide coatings can be easily obtained by using an electrolytic bathmaintained at room temperature, and therefore the bath can be easilycontrolled. Accordingly, in the method of the present invention,aluminous materials can be treated in the same manner as in the case ofconventional anodic oxidation process. Moreover, the oxidized coatingobtained by the method of the present invention is excellent in the corrosion resistance, abrasion resistance and weather resistance.

What is claimed is:

1. A method of producing colored oxide coatings ranging from yellow tobrown on aluminum or aluminum alloy, which consists essentially ofelectrolytically anodizing with direct current, an aluminum materialselected from the group consisting of aluminum and an alloy thereof inan aqueous solution of 0.5 10.0 percent by weight of oxalic acid and0.05 4.0 percent by weight of a salt selected from the group consistingof ammonium phosphate, ammonium dichromate, a metal acetate and a metalnitrate at a temperature of between 0 and 50C; a voltage of between5-160 volts, a current density of between 0.05 5 A/dm and for a time ofbetween 10-120 minutes.

2. A method as claimed in claim 1, wherein said acetate is. selectedfrom the group consisting of manganese acetate and chromium acetate.

3. A method as claimed in claim 1, wherein said metal nitrate isselected from the group consisting of ferric nitrate and chromiumnitrate.

4. A method of producing colored oxide coatings ranging from yellow tobrown on aluminum or aluminum alloy, which consists essentially ofelectrolytically anodizing with direct current, an aluminum materialselected from the group consisting of aluminum and an alloy thereof inan aqueous solution of 0.5 10.0 percent by weight of oxalic acid and0.05 4.0 percent by amount of said ammonium salt is 0.05 4.0 percent byweight.

6. A method asclaimed in claim 1, wherein the amount of said acetate is0.05 1.5 percent by weight.

7. A method as claimed in claim 4, wherein the amount of said metalnitrate is 0.05 0.7 percent by weight.

2. A method as claimed in claim 1, wherein said acetate is selected fromthe group consisting Of manganese acetate and chromium acetate.
 3. Amethod as claimed in claim 1, wherein said metal nitrate is selectedfrom the group consisting of ferric nitrate and chromium nitrate.
 4. Amethod of producing colored oxide coatings ranging from yellow to brownon aluminum or aluminum alloy, which consists essentially ofelectrolytically anodizing with direct current, an aluminum materialselected from the group consisting of aluminum and an alloy thereof inan aqueous solution of 0.5 - 10.0 percent by weight of oxalic acid and0.05 - 4.0 percent by weight of a salt selected from the groupconsisting of ammonium phosphate, ammonium dichromate, manganeseacetate, chromium acetate, ferric nitrate and chromium nitrate at atemperature of between 0* and 50*C; a voltage of between 5-160 volts, acurrent density of between 0.05 - 5 A/dm2, and for a time of between10-120 minutes.
 5. A method as claimed in claim 4, wherein the amount ofsaid ammonium salt is 0.05 - 4.0 percent by weight.
 6. A method asclaimed in claim 1, wherein the amount of said acetate is 0.05 - 1.5percent by weight.
 7. A method as claimed in claim 4, wherein the amountof said metal nitrate is 0.05 - 0.7 percent by weight.